The effect of Vesicular - Arbuscular Mycorrhiza on growth,yeild and incidence of diseases on tomatoe(lycopersicon esculentum Mill.) in Zambia
Masuwa, Linen Mulala
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Mycorrhizae are obligate symbionts which enhance plant growth and protect plants from certain diseases. The mycorrhizal flora of three soils collected from a virgin land at the University of Zambia School of Agriculture Experimental site, Airport and the State lodge consisted of Glomus etunicatum, Glomus fasciculatum and Acaulospora scrohiculata. This composite mycorrhizal flora was used to determine the effect of vesicular-arbuscular mycorrhiza (VAM) on the growth, yield and incidence of Septoria leaf spot, caused by Septoria lycopersici, and Fusarium wilt, caused by Fusarium oxysporum f. sp. lycopersici on tomato (Lycopersicon esculentum Mill.). The experiment was carried out during the 2000/2001 growing season in the greenhouse at the experimental field of the School of Agriculture, at the University of Zambia and in two field experimental sites, one at the School of Agriculture Field Station and the other at Mount Makulu Central Research Station, Chilanga. The VAM flora was multiplied for a period of 8 weeks by planting surface disinfected maize seeds of the variety MMV 600 in heat sterilized soil. This VAM soil inoculum was mixed in proportions of 3 VAM soil inoculum to 1 sterilized soil (high level), 1 VAM soil inoculum to 1 sterilized soil (medium level) and 1 VAM soil inoculum to 3 sterilized soil (low level). Surface disinfected seeds of the Floradade tomato were planted in these soil mixtures in plastic pots and in seedling beds later to be transplanted to the field for field experiments. A Randomized Complete Block Design (RCBD) with 3 treatments and 1 control was used. Tomato plants were periodically examined to measure plant height, stem diameter, number of leaves, number of days taken to flowering, number of aborted flowers, dry shoot and root weight and tomato plant yield.Studies on disease incidence of Septoria leaf spot involved spraying 2 ml conidial suspension of Septoria lycopersici on each plant at the flowering stage. The 2 ml conidial suspension of Fusarium oxysporum f sp. lycopersici was sprayed at the shoot-root interface when plants were 90 days old from planting. The disease incidence for Septoria leaf spot was studied by monitoring disease progress at one week interval for one month and Fusarium wilt by weighing the fresh root weight at the end of the experiment.The analysis of variance (ANOVA) of the measured parameters indicated that VAM enhanced the growth and development of tomato by 53%. The plant yield was increased by 38%. To achieve this tomato crops should be inoculated with suitable VAM fungi before transplanting them to the field. High mycorrhizal levels (3 VAM soil inoculum to 1 sterilized soil) resulted in reduced plant growth during the early stages of fungal establishment. The results showed that 1 part of inoculum to 1 part of sterilized soil (medium mycorrhizal level) was better than high levels.The results also showed that there was 8% reduction of disease incidence of Septoria leaf spot and 10% reduction of Fusarium wilt in tomato treated with VAM inoculum. However, the use of high levels of VAM inoculum is not advisable for the control of Septoria leaf spot since the fungi deprive the plant of the required photosynthates.